ASRock B75M Good for Gaming?

Yes that will be fine.

The only drawback to this motherboard is that since it is the b75 chipset, you will not have turbo boost or OC potential at all.

would you computer be a bit weaker compared to others? yes if your processor is one that has turbo boost or OC potential. It will only run at max stock speed

for example an i5 2300 will run at 2.8 ghz but can turbo boost up to 3.2 ghz. With this mother board you won't be able to hit the 3.2. Is this a big deal? no not for a budget gaming computer at all

Will this effect your games. No not really.